1. Field of the Invention
The present invention relates to a magnetic head assembly for recording tape, such as quarter-inch tape, and more particularly to a multi-element magnetic head assembly in which the servo elements are decoupled from the read elements.
2. Description of the Related Art
Quarter-inch tape is especially useful for backing up data generated on a computer. Generally 10 to 13 gigabytes of data may be stored on a quarter-inch tape, the tape generally being contained within a quarter-inch cartridge referred to in the industry as QIC. A 10 gigabyte QIC would be known as a QIC-10. Because of the large amount of backup data that is stored by virtually any computer equipped office and even by users of home computers, it is desirable that as much backup data as possible be packed per unit area of the magnetic tape. There are three major techniques to maximize packing density, namely: (1) reduction of track widths, (2) increasing linear recording density and (3) optimization of the layout of data and servo tracks on the tapes.
As is known, a magnetic head assembly for a tape drive combines write and read elements in an integrated structure that provides the capability of writing and reading multiple tracks on a moving tape. The size of a write element determines how many bits of data can be written per square inch of tape. More particularly, the length of the gap of the write element limits linear density of information written by the head and the width of the gap determines the track density of information written by the head. The product of these two parameters is areal density. Areal density indicates the density with which information may be stored on the tape and is expressed in bits per square inch.
The layout of data and servo tracks on a tape is determined by the arrangement of the elements on a head surface of a head assembly. The head assembly typically contains multiple write, read and servo elements. The write elements have a magnetic record gap and the read and servo elements are magneto-sensitive transducers which have a magnetic read gap and a magnetic servo gap respectively. The write element gaps and read/servo transducers gaps form a part of the head surface which faces a magnetic tape. The gaps are normally aligned along one or more gap lines, each gap line lying in a respective plane that defines a head assembly module which may be joined to one or more other modules during fabrication. A three-module head assembly with a write gaps and a read gap are located on a common data lines. Additionally, first and second servo gaps are located in each gap line on a common servo line. This is typical for processing quarter-inch tape. Data is first written to a track in a forward direction. In the prior art the tape may then be reversed so that data is written to an adjacent track. The tape is reversed again to move in the forward direction to write to the next adjacent track, and so on. A significant problem with this mode of data recording is known as "double track squeeze". In this regard, a data track is effectively narrowed ("squeezed") by adjacent data tracks above and below it which are written in a direction that is opposite to the data track being squeezed. In each direction of travel, the tape has an inherent signature of lateral movement which does not match the signature in the opposite direction. The signatures of two outer tracks encroach upon the edges of a sandwiched track, narrowing the effective width of the sandwiched track. In order to eliminate double track squeeze, it is necessary to increase the track pitch, which then decreases the areal density of the quarter-inch tape.
A typical three-module head assembly may employ read elements for the dual purpose of reading and servoing. This makes the width of the gap of the read element dependent upon the width of the gap needed for servoing, which is typically larger than that required for reading. Increasing the width of the read element gap requires wider write element gaps because tracks are normally written wider than the gaps of read elements to provide a track misregistration margin. This is referred to as "write wide and read narrow". This dependency also increases the required pitch of the tracks and results again in less areal density. It would be highly desirable to decouple the reading and servoing functions from a single read element, and perform these functions separately with separate elements. With such a decoupling, the data track/servo track arrangement can be optimized to increase the areal density of the quarter-inch tape. Decoupling would also allow increased flexibility in the design of guard bands without affecting track pitch.
Other problems are associated with the prior art three-module head assembly. Each module is constructed separately with read elements in one module, write elements in a second module, and read elements in a third module. The modules are joined during fabrication to produce the integrated head assembly. Each module has a gap line for the alignment of magnetic elements. When the modules are joined together, it is difficult to align the elements on a common track with a tolerance of 3 .mu.m or less. This results in track misregistration (TMR) which is especially apparent between gap lines. This problem has been solved in the past by increasing track pitch. This, however, reduces the areal density of the tape. It would be desirable to provide an arrangement for compensating for TMR due to the inaccuracy of joining modules during fabrication. Further, it would be desirable if this same arrangement would compensate for tape skew, which is inherent in each magnetic tape drive and which produces the same effect as TMR. Further, it would be desirable if the head assembly could be made from two modules instead of three in order to reduce the cost of construction.
Another problem with prior art head assemblies has been the inability to stay on track when a servo element encounters longitudinal scratches or defects along a servo track. When this occurs, the track may be lost and a considerable amount of data may not be written. It is highly desirable to maintain tracking even when a servo element encounters a longitudinal scratch or defect along the servo track.
The prior art head assemblies also constrain the width of the write elements. Because of the close proximity of magnetic elements along a gap line, the width of the write elements must be limited, which in turn requires two or more layers of coils in the write element to generate sufficient flux to write reliably. Double deck coil configurations are expensive. It would be desirable if sufficient width could be provided for the write head so that a single layer of coils could be fabricated.